The present invention relates to conveying devices, and more particularly to roller conveyors that employ multiple conveyor rollers side-by-side.
Roller conveyors, also known as roll conveyors, have for many years been used to convey a wide variety of objects and bulk materials. For example, U.S. Pat. No. 1,725,740 (Schulte) features a conveyor for metal rolling mills. Several spaced apart rollers, each journalled in bearings supported on a stationary frame, define a horizontal transport path. Each roll is driven by its own electric motor. Present day roll conveyors are generally similar, although some systems intersperse idler rollers with drive rollers, and other systems have a chain or a belt that links a common drive to all rollers or groups of rollers.
While the present invention is not limited to the handling of any particular material, this disclosure is specifically directed to a roller conveyor for handling taconite (iron ore) pellets. One of the necessary process steps in handling taconite is to harden or fire the taconite pellets. Typically a roller conveyor feeds the green, unfired pellets to a grate where firing takes place. Firing converts the fragile green pellets to hardened pellets more suitable for their transport to steel mills.
Roller conveyors gently convey the green pellets toward the firing grate. The individual rollers are spaced apart from one another in the transport direction to define gaps between adjacent rollers. Fine pellets and dust fall through the gaps and are recirculated back to a balling area for further processing. Consequently, firing and pollution problems due to dust and fine particles are reduced.
Present day roller conveyors for taconite use rollers typically 12-20 feet long, and diameters typically 4-8 inches. Given a particular roller diameter and spacing between adjacent rollers, the number of rollers employed is determined by the desired length of the transport path, and usually is in the range of 15 to 40.
FIG. 1 illustrates a conventional roller and its support and drive arrangement. More particularly, a cylindrical roller 1 is mounted concentrically on a rotating shaft 2 that extends in both axial directions from the roller. The shaft is supported rotatably by two pillow block bearings 3 and 4, and driven by an enclosed fan cooled motor 5 through a right angle reducer 6.
When in use, the roller conveyor is subject to extreme conditions involving excessive dust, high temperatures and considerable fluctuations in temperature. The motor bearings, reducer and other couplings are subject to the dust. Also, when roller 1 and shaft 2 thermally expand responsive to temperature increases, the shaft applies axial thrust loads to the pillow block bearings, causing premature bearing failure. Failure does not prevent the rollers from continuing to operate. However, it does lead to variance in the gap width between adjacent rollers, either increasing or reducing the percentage of fine particles falling between rollers, in either case leading to a lower quality product.
Therefore, it is an object of the present invention to provide a roller conveyor in which the roller support and drive components experience less exposure to dust and fine particulates.
Another object is to provide a roller conveyor in which individual rollers and their respective support components accommodate thermal expansions and contractions.
A further object is to provide, in a conveyor with multiple side-by-side rollers, a support system that more positively maintains the individual rolls concentric on their rotational axes, to more precisely maintain a predetermined spacing between adjacent rollers.
Yet another object is to provide a simpler and more reliable roll conveyor.